论文标题
在宽轨道中动态形成极低的质量白矮人二进制
Dynamically Forming Extremely Low-Mass White Dwarf Binaries in Wide Orbits
论文作者
论文摘要
在宽轨道（约450天）中检测0.2 MSUN极低质量的白矮人（EW），其主要距离（MSUN）主序列（MS）伴侣KIC 8145411，挑战了我们当前对EWS形式的理解。通过来自WD祖细胞的传质，EW形成的传统渠道有望在紧密的轨道中形成EW二进制文件。实际上，大多数已知的EWS都是在中间porb约5.4小时的紧密二进制中发现的。使用数值散射实验，我们发现恒星簇中的二元二元强遇到可以充分扩大典型的EW二进制的轨道，以解释观察到的KIC 8145411系统的宽轨道。通过二元二进制遇到产生的EW二进制的PORB分布是双峰的：一种模式对应于EW二进制的初始轨道周期，而另一个模式接近PORB大约100天，类似于KIC 8145411系统的轨道周期。我们发现，宽阔的EW二进制文件的产生也被从簇峰值弹出的星簇质量约为10^5 msun，速率约为10^{ - 3} gyr^{ - 1}。假设所有恒星中有50％的恒星簇形成，并且与M^{-2}成比例的初始簇质量函数，我们估计宽EW二进制文件的银河系形成速率约为4.16 x 10^3 Gyr^{ - 1}。
The detection of a 0.2 Msun extremely low-mass white dwarf (EW) in a wide orbit (Porb about 450 days) with a 1.1 Msun main-sequence (MS) companion, KIC 8145411, challenges our current understanding of how EWs form. The traditional channel for EW formation, via mass transfer from the WD progenitor, is expected to form EW binaries in tight orbits. Indeed, the majority of known EWs are found in tight binaries with a median Porb about 5.4 hrs. Using numerical scattering experiments, we find that binary-binary strong encounters in star clusters can sufficiently widen the orbit of a typical EW binary, to explain the observed wide orbit of the KIC 8145411 system. The Porb distribution for EW binaries produced through binary-binary encounters is bimodal: one mode corresponds to the initial orbital period of the EW binary, while the other is near Porb about a few 100 days, similar to the orbital period of the KIC 8145411 system. We find that the production of wide EW binaries that are also ejected from the cluster peaks at a star cluster mass of about 10^5 Msun with a rate of about 10^{-3} Gyr^{-1}. Assuming that 50% of all stars form in star clusters and an initial cluster mass function proportional to m^{-2}, we estimate a galactic formation rate of about 4.16 x 10^3 Gyr^{-1} for wide EW binaries.
